Finnish patent application 944287 discloses the type of water purification device described above comprising a membrane-structured filtering part. The solution in question is meant to operate by so called syphon principle, thanks to which the structure of the same is very simple. The water purification device in question is very safe and easy to use in practice, because the quality of the water flowing to the collecting point thanks to the syphon phenomenon being self-powered is continually homogeneous regardless of the operating time of the device. This is first of all based on the fact that a water purification device equipped with a thin PTM- or TeM-filtering film does not at any stage let through material parts exceeding a certain particle size, in which case, when the filtering film gets dirty, only the penetration speed of the filter decreases and may even totally be interrupted, in case the filtering film is not cleaned every now and then.
The device described above is very useful in most heterogeneous connections, e.g. in terrain for filtering of lake water or under other circumstances as well, wherein actual tap water may not be used. One disadvantage of the device is mainly the slowness of the filtering speed and on the other hand also the fact, that e.g. in ordinary household use the device requires use of separate vessels, so that functioning of the syphon phenomen could be brought out. In practice, cleaning of the filtering film of the device in question is disadvantageous to a certain extent as well, because it must be carried out first of all manually as a totally separate stage of operation. Manual cleaning of the filtering film is on the other hand disadvantageous in such respect as well, that during mechanical rubbing by too "heavy-handed" treatment the pores in the filtering film may get enlarged unintentionally or on the other hand they may get stuffed up by impurities. This is why, functioning of the filtering film of a device being used under particularly dirty circumstances, may weaken too much immediately after the first cleaning measure due to decreased penetration ability. A crucial disadvantage involved with the type of apparatus in question may be in practice, however, the fact, that it is not possible to exploit the same as such very simply, e.g. for filtering of water being led directly from a water distribution system, but instead separate water vessels must be used because of the syphon principle.
On the other hand from e.g. Japanese application 5-177 185 it is known to exploit a membrane-structured filtering device, that is placed to a basin comprising liquid to be treated. The solution in question is thus meant for large-scale use, but in principle a corresponding type of solution may be placed e.g. directly at the end of a supply pipe as well. In the solution in question the filtering means are brought out by a so called bag filter principle in a way, that liquid to be treated goes through the walls of the elongated membrane pipes to the secondary side of the filter keeping clean water and furthermore for some utility purpose through a flow-way being connected to this side. The solution in question is advantageous in such respect, that for purifying of the filtering means there has been exploited an inverse flushing flow, in which case at the secondary side of the filter there has been placed a supplementary container keeping filtered water. In this case, when running of water is interrupted, a pump is being used, which feeds the filtered water from the supplementary container as an inverse flow through the filtering pipes, whereby the same get purified.
The arrangement in question is advantageous in such respect, that the porous structures of the filtering pipework may be flushed by means of an inverse flow. In practice, the type of elongated, flexible pipe structures as described above collect, however, impurities particularly to the outer surfaces of the same, that is why e.g. bacteria growth may get collected to the same, that may not be, however, influenced directly by means of the type of inverse flow described above. This is why the flushing principle in question operates only partly. In addition to that, the type of solution has such a disadvantage as well, that the filtering pipework is a very confused entirety, that is why it is not possible to get any kind of sight inside the same, in which case e.g. fungus or some other corresponding undesired bacteria formulation being generated therewith may not be noticed. The solution in question is on the other hand disadvantageous in such respect as well, that a separate pump must be used for the purification flushing, which requires a very complicated control and adjustment automation and instrumentation. This for its part makes use of the device more difficult and decreases efficiency of the same decisively in practice as well.
Thus, nowadays there are not any water purifiers or like on the market, that would be profitable enough by the acquisition or functional costs and that would be technically easy to utilize e.g. for household use and, that would operate effectively enough and eliminate particularly bacteria under all kinds of circumstances reliably enough.